You sweat in the back of the truck, feeling it bounce around outside, and contemplate your situation. Suddenly, the truck comes to a shuddering halt, and you bang your head against the roof. There is a faint light as the trunk opens, and the biker glares down at you. He pulls you out and pushes you to the ground.
'So, kid, I've been thinkin' on the drive. A slave might bring me more attention than I want right now, but there are alternatives...'
He crouches down and grins at you.
'Bark for me doggy.'
You pause, confused, and the biker kicks you squarely in the chest. You are knocked back, winded, and look up at his glare.
'Do it, dog!'
Humiliated, you bark like a dog for him. He grins.
'Now, roll over.'
You do so, rolling naked over the wet grass, and he pulls a dog biscuit from an inside pocket, tossing it to you. Instinctively, you catch it in your mouth. The taste isn't bad. You begin to feel less worried as your master runs you through several dog tricks, tossing you dog biscuits each time.
He pats you on the head, and you yip happily. You feel an odd itch, and scratch at your chest, only to find a thick growth of white hair. You look up at him, confused.
'See, a slave is odd, but its perfectly normal for a guy to own a dog. You want to me my doggy, don't ya? You don't have to worry; I can fuck you just as hard either way.'
You are surprised to find that yes, you do want to be his dog. You pant as the fur spreads across your chest. When it reaches your crotch, you growl at a surge of sexual pleasure as your cock turns pointy and red, pulling up into a furry sheath.
Your feet begin to swell as your toes fuse into thick digits with small black claws. The base of your spine extends and grows into a large, furry tail as the fur covers your whole body, and your arms and legs snap into a suitably canine position. Your mouth pushes forward into a canine muzzle and your teeth grow sharp and long, and your ears perk up into furry points.
Your vision turns monochrome but is replaced by a new world of powerful smells; particularly that of your master; his sweat is overwhelming and erotic.
The biker rubs your head, grinning, and clips a dogtag to your collar. Then he lies back on the grass, unzipping his pants to reveal his hard cock.
'Damn if that didn't turn me on. It ain't bestiality is you used to be human; suck it, pooch.'
Gratefully, you jump forward, lapping and suckling at your masters hard cock, relishing the salty sweaty taste. With a roar, he comes into your muzzle, and with the bitter taste your mind changes so that you only remember life with your master, as his loyal pet dog.